The present invention relates to image forming apparatuses using the electro-photographic method, such as copiers, printers, and facsimile machines, and, in particular, relates to the cleaning means in such apparatuses for removing the toner remaining on the image carrier.
The blade cleaning method is known which is a cleaning method used in an image forming apparatus with a configuration of forming the toner image on a photosensitive member (photoreceptor) having around it various means for charging, exposure, and development, then either directly transferring the toner image onto the transfer medium, or transferring the toner images from plural photosensitive bodies temporarily-onto an intermediate image transfer body and then making a secondary transfer of the toner image on the intermediate image transfer body onto a transfer member, with said cleaning method of removing the toner remaining on the secondary transfer body or on the intermediate image transfer body (both of which are collectively called an image carrier or an image carrying member) by making a blade made of an elastic material such as urethane (hereinafter called the cleaning blade) press against the image carrier in a direction counter to the direction of movement of the image carrier.
In the blade cleaning method, since it is necessary to make the cleaning blade press against the image carrier with a force equal to or greater than a specific value order to scrape off the toner surely, friction is generated between the cleaning blade and the image-carrier and this friction causes problems such as bending of the cleaning blade, damage to the cleaning blade edge, toner filming, and pitch variations of the image caused by changes in the image carrier driving force due to increased friction force.
Toner is structured by a mixture of base materials and external additives, and the base materials are for example pigment, wax, resin, and the external additive is composed of abrasive particles and lubricant such as silica and titania which impart electrification.
When remaining toner is removed from an intermediate image transfer body by a cleaning blade, a part of toner still remains on the edge, though the remaining toner is scraped by the edge of the cleaning blade. Abrasive particles contained in the remaining toner also works as a lubricant, and works to reduce the friction coefficient between the cleaning blade and the intermediate image transfer body by means of insertion of a small amount of them into a clearance between the edge and the intermediate image transfer body, and consequently the blade can continue to remove the remaining toner without being bent.
However, wax and lubricant contained in toner partially adhere to the intermediate image transfer body and makes a thin film by being extended without being removed sufficiently to cause a so-called filming phenomenon in the traveling direction of the intermediate image transfer body.
Further, though it is needed for toner to always gather on the edge, a shortage of toner happens if many copies with low printing ratio, on which a copied image is formed partially, are produced. In case of a shortage of toner, the friction coefficient between the cleaning blade and the intermediate image transfer body rises, and parts of edge where it is short of toner, get damage and hence the wax and lubricant slip under the damaged portion of cleaning blade thereby causing-toner filming.
When a filming phenomenon occurs on an intermediate image transfer body, electric resistance rises at the portion, and electric charge is conducted preferentially into portions where no toner filming occurs in the primary image transfer and the secondary image transfer. Therefore, the image transferability at the portion where toner filming occurs deteriorates, and causes white striations on a recording material.
The following patent documents have been disclosed.
[Patent Document 1] TOKKAI No. 2002-268400
[Patent Document 2] TOKKAI No. HEI5-40438
[Patent Document 3] TOKKAI No. HEI6-318019
[Patent Document 4] TOKKAI No. HEI7-104627
In Patent Document 1, there has been disclosed a image forming apparatus having a cleaning member which uses simultaneously a function cleaning remaining toner on a intermediate image transfer body by means of indirect bias charging with a cleaning bias charging member and a function applying lubricant to a intermediate image transfer body.
A proposal in Patent Document 2 is that of preventing the generation of the above problems by detecting the quantity of toner supplied to the developing unit from the toner supply container section, and depending the result of that detection, sending the image carrier to the cleaning section after forcibly coating it with toner.
This is based on the thinking that the quantity of toner consumed by the image carrier is proportional to the quantity of toner supplied to the developing unit, and if more toner is made to be consumed by the image carrier, the quantity of toner sent to the cleaning section is compulsorily made smaller, and, on the other hand, the control is carried out so that the quantity of toner sent to the cleaning section is made larger if the quantity of toner consumed is smaller.
A proposal in Patent Document 3 is that of preventing the generation of the above problems by detecting the extent of mirror-like condition of the surface of the photosensitive body which is an image carrier, and when the surface of the photosensitive body is highly mirror-like, a high density toner image is formed covering the non-image part of the photosensitive body before the body is sent to the cleaning section, thereby lowering the friction between the photosensitive body and the cleaning blade.
In a proposal in Patent Document 4, the cleaning blade is made to press against the image carrier in a direction counter to the direction of movement of the image carrier, and also, the front edge of the surface pressing against the photosensitive body is made to have a shape so that it recedes in the direction of the movement of the image carrier more and more at locations near the two side edges of the image carrier, that is, from the central part which is the image formation area where the toner image is formed towards the non image forming area at the two sides of the image forming area, thereby transporting the toner scraped off from the central toner image forming area to the non image forming area with the intention of reducing the friction force between the cleaning blade and the image carrier body in the on image forming area.
However, it has not been disclosed that an appropriate quantity of toner is supplied to a clearance between a cleaning edge and an image carrying member (a photoreceptor or an intermediate image-transfer body) in Patent Document 1.
In the method described in the Patent document 2, since the information in the width direction of printing has not been considered, in case the printing width is small and also high density toner image is formed consecutively, the amount of toner consumption will be judged to be high and the quantity of toner supplied to the cleaning section will forcibly be made smaller.
As a consequence, the quantity of toner present as lubricant in the non-printing area becomes insufficient, thereby causing the problems described above such as bending of the cleaning blade, damage to the cleaning blade edge, toner filming, and pitch variations of the image, etc.
In the method described in the Patent document 2, the extent of mirror-like nature of the surface of the photosensitive body in the direction along the axis of rotation will be affected by the history of the printing width. In other words, there will be the problem that the mirror-like nature of the part of the surface of the photosensitive body that is printed commonly irrespective of the printing width will be increasing with more and more use, but the mirror-like nature of the part of the surface of the photosensitive body that is not used much will not increase with time of use. Because of this, if the toner is supplied forcibly to the cleaning section based on the extent of mirror-like nature of the surface of the part of the surface of the photosensitive body that is not used much, the quantity of toner will become insufficient in the part of the surface where the extent of the mirror-like nature has increased, and hence causing the problems described above. On the other hand, if the quantity of toner supplied to the cleaning section forcibly is increased based on the extent of mirror-like nature of the commonly printed part of the photosensitive body, unnecessary quantity of toner will be supplied to the part of the surface where the extent of mirror-like nature has not increased substantially, thereby wastefully consuming the toner.
Further, in the two methods described in Patent documents 2 and 3, since the toner is fed to the cleaning section forcibly, there are simultaneous problems of more time becoming necessary for forming the image thus lowering the productivity and wasteful consumption of the toner if image forming is carried out frequently.
In the method described in the Patent document 4, if toner images with small printing width and low printing ratio are formed consecutively, the quantity of toner removed by the cleaning blade becomes smaller and hence the toner may not reach the two ends of the cleaning blade.
In addition, the hardness of the cleaning blade decreases near its two ends and hence the toner slips under the cleaning blade thereby causing cleaning defects.